.front {
  width: 20px;
  height: 20px;
  background-color: #fff;
}

.back {
  background-image: url('joystick.png');
  background-size: cover;
}

#nipple_1_1 .back {
  background-image: url('button.png');
  background-size: cover;
}

#left {
  position: relative;
  width: 20%;
  height: 100%;
  background-color: #ccc;
}
#right {
  position: relative;
  width: 20%;
  height: 100%;
  background-color: #ccc;
}